Remote copy which is data copy between first and second storage apparatuses is known. Types of remote copy are, for example, synchronous remote copy and asynchronous remote copy. If the first storage apparatus receives a write request from a host and if synchronous remote copy is adopted, after the data complying with the write request is transferred from the first storage apparatus to the second storage apparatus, a write completion response is transmitted to the host apparatus while, if asynchronous remote copy is adopted, even if the data complying with the write request is not transferred from the first storage apparatus to the second storage apparatus, the write completion response is transmitted to the host apparatus.
In a remote copy system to which asynchronous remote copy is adopted (hereinafter referred to as an asynchronous remote copy system), for example, the first storage apparatus comprises, as well as a first DVOL (a data volume which is a logical volume in which the data is stored), a first JVOL (a journal volume which is a logical volume in which a journal (hereinafter referred to as a JNL) is stored). Similarly, the second storage apparatus comprises a second JVOL as well as a second DVOL. The first storage apparatus, if receiving a write request, stores the data complying with the write request in the first DVOL and, at the same time, stores the JNL of the data in the first JVOL. The first storage apparatus transfers the JNL in the first JVOL to the second storage apparatus, and the second storage apparatus writes the JNL from the first storage apparatus to the second JVOL. After that, the second storage apparatus writes the data which the JNL in the second JVOL comprises to the second DVOL. By this method, the data written to the first DVOL is considered to have been copied to the second DVOL.
In Patent Literature 1, an asynchronous remote copy system with a multihop (cascade) method is disclosed. In the multihop method, three or more storage apparatuses are serially connected, of which the storage apparatus as the starting point is the copy source while the storage apparatus as the ending point is the copy destination, and the intermediate storage apparatuses existing between the starting point and the ending point are both the copy source and the copy destination.
As more specifically described, in the Patent Literature 1, for example, the items below are disclosed.
(*) The first storage apparatus, the second storage apparatus, and the third storage apparatus exist.
(*) The first storage apparatus is the copy source, the third storage apparatus is the copy destination, and the second storage apparatus exists between the first and the third storage apparatuses, and is both the copy source and the copy destination.
(*) The first storage apparatus comprises a first DVOL and a first JVOL.
(*) The second storage apparatus comprises a second DVOL, a first second JVOL, and a second JVOL.
(*) The third storage apparatus comprises a third DVOL and a third JVOL.
(*) The first and the second DVOLs are paired. The first DVOL is the primary DVOL (PVOL), and the second DVOL is the secondary DVOL (SVOL).
(*) The second and the third DVOLs are paired. The second DVOL is the primary DVOL (PVOL), and the third DVOL is the secondary DVOL (SVOL). That is, the second DVOL is an SPVOL which is both the PVOL and SVOL.
(*) A first host apparatus writes the data to the first DVOL.
(*) The first host apparatus updates an update number.
(*) The first storage apparatus writes the JNL of the data written to the first DVOL to the first JVOL. The JNL, as well as the data which is the input/output target of the host apparatus, includes the update number.
(*) The JNL in the first JVOL is copied to the first second JVOL.
(*) The second storage apparatus reflects one or more JNLs in the first second JVOL which are not reflected in the second DVOL in order of the update numbers (writes the data which the JNLs comprise to the second DVOL).
(*) The second storage apparatus writes the JNL including the data in the JNLs reflected in the second DVOL to the second second JVOL.
(*) The JNL in the second JVOL is copied to the third JVOL.
(*) The third storage apparatus reflects one or more JNLs in the third JVOL which are not reflected in the third DVOL in order of the update numbers.